Rotation of visual content on a display unit

ABSTRACT

A graphics presentation apparatus including a display unit, an eye-tracking module, and a data output module. The eye-tracking module registers image data representing at least one eye of a user of the apparatus. Furthermore, the eye-tracking module determines, based on the registered image data, an orientation of the at least one eye relative to the display unit. Finally, in response thereto, the eye-tracking module generates a control signal controlling the data output module to produce visual content with such orientation on the display unit that a misalignment between the orientation of said at least one part and the orientation of the at least one eye of the user is minimized.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of Non-Provisional U.S. patentapplication Ser. No. 15/628,193 filed Jun. 20, 2017, which is acontinuation of Non-Provisional U.S. patent application Ser. No.14/103,336 filed Dec. 11, 2013, which claims priority to European PatentApplication Number 12196926.5 filed Dec. 13, 2012, the entiredisclosures of which are hereby incorporated by reference, for allpurposes, as if fully set forth herein.

THE BACKGROUND OF THE INVENTION AND PRIOR ART

The present invention relates generally to solutions for presentingvisual data to the user of a computing and/or communication apparatus.More particularly the invention relates to an apparatus, method, andcomputer program product for a graphics presentation apparatus and amethod for presenting visual context on a display unit of the graphicspresentation apparatus.

Today, the user interaction with a computing and/or communication devicecan be made fairly flexible and intuitive. For example, there arenumerous of solutions that cause the format in which information isdisplayed to vary depending on how the device is positioned and/orrepositioned during the interaction in order to improve the efficiencyand usability of a user interface.

U.S. 2010/0188328 describes an environmental gesture recognition system,wherein specific motion patterns are interpreted as commands to a datasystem. For instance, flipping a portable device backwards may representa scroll-down command and flipping the device forwards may represent ascroll-up command, while rotating the device clockwise orcounter-clockwise around its vertical axis may represent commands forselecting a next and a previous page respectively of a displayeddocument.

U.S. 2012/0001943 discloses a system, wherein a sensor determines astate of tilt changes of an electronic device. In response to a tiltdirection and a tilt angle, the system controls how information ispresented on a display unit of the electronic device.

U.S. 2004/0157647 describes a portable device with a display, which isassociated with a rotation detection device for detecting thedisplacement of a housing that stores the display. As a result, when theportable device is rotated 90°, an image shown on the display can berotated 90° so as to compensate for the rotation of the device.

U.S. 2012/0229371 reveals screen rotation lock methods for preventing anangle-dependent auto rotation of the information that is displayed onthe screen of a portable device. Thus, for example, a user can choose toavoid that the screen content is rotated when the device is rotated(e.g. as in U.S. 2012/0001943 or U.S. 2004/0157647).

U.S. 2012/0235790 relates to a solution for locking and unlocking amobile device using facial recognition. Here, the camera of the devicecaptures images, and a face recognition processor determines whether ornot a user is present in front of the device. If not, the device islocked. This function may be triggered in response to the fact that thedevice has been motionless for a threshold time.

The article Chen, L. P. et al., “iRotate: Automatic Screen Rotationbased on Face Orientation”, Session: Phone Fun: Extending MobileInteraction, CHI'12, May 5-10, 2012, Austin, Tex., USA, pp 2203-2210reveals an approach to automatically rotate the screen content on amobile device to match a user's face orientation. Here, the front cameraof the mobile device, such as a mobile phone or tablet, is used todetect the user's face and causes the screen content to rotateaccordingly. Thus, in contrast to gravitation-based rotation, thecontent will be presented correctly also for a user lying down on oneside while interacting with the device.

PROBLEMS ASSOCIATED WITH THE PRIOR ART

Although the above solutions may facilitate the general user interactionwith an electronic apparatus, there is still room for improving thevisual data presentation. For example the above-mentioned locking andunlocking solution may be annoying to a user because he/she may eitherforget to activate or deactivate the function, and therefore the visualinterface does not behave as expected. Moreover, the solutions that relyon image registration of a user's facial features may fail if the user'sface is partially obscured by an object between the device and the userand/or if the device is operated in dim light.

SUMMARY OF THE INVENTION

The object of the present invention is to mitigate the above problems,and thus offer an improved solution for presenting visual content in auser-friendly manner on the display unit of a graphics presentationapparatus.

According to one aspect of the invention, the object is achieved by theinitially described graphics presentation apparatus, wherein aneye-tracking module is included, which is configured to register imagedata representing at least one eye of a user of the apparatus. Based onthe registered image data, the eye-tracking module is further configuredto determine an orientation of the at least one eye of the user relativeto the display unit. In response thereto, the eye-tracking module isconfigured to generate the control signal so that it controls the dataoutput module to produce the visual content in such a manner that amisalignment between the orientation of at least one part of the visualcontent and the orientation of the at least one eye of the user isminimized.

This apparatus is advantageous because it provides an intuitive andeffortless adaption of a visual user interface to a user's behaviorirrespective of whether the physical equipment is repositioned, the userchanges his/her posture or if a certain piece of information (e.g. animage or a text section) is retrieved for presentation, which has adefault orientation that does not match the current orientation of theuser's eyes. Moreover, the proposed apparatus works reliably also if theuser's face is partially obscured, or covered, e.g. by a piece ofclothing. In fact, it is sufficient if as little as one eye of the useris visible.

According to one preferred embodiment of this aspect of the invention,the data output module is configured to produce the visual content withan orientation relative to the display unit, which orientation may onlybe varied in predefined angular increments. For example, the incrementsmay represent 90 degree steps, such that the visual content can attainfour different orientations on the display unit. Namely, this is verywell suited for a rectangular shaped display unit.

According to a further preferred embodiment of this aspect of theinvention, the graphics presentation apparatus includes a rotationdetection module configured to register an attitude angle of the displayunit relative to a frame of reference external to the graphicspresentation apparatus, e.g. the Earth's field of gravitation. The dataoutput module is further configured to produce the visual content insuch a manner that the visual content is presented with an orientationand a format that depends on the attitude angle of the content relativeto the frame of reference. Thereby, in a device where the orientation ofthe display unit may vary over time (e.g. a portable device), by defaultthe orientation of the visual content may be controlled by the visualcontent's orientation relative to the external frame of reference. Thus,the eye tracking function can be activated exclusively when it is deemedrelevant to perform measurements of the eye orientation.

According to another preferred embodiment of this aspect of theinvention, the rotation detection module is configured to generate atrigger signal if the content angle has exceeded a threshold anglerelative to the frame of reference during a threshold time. The eyetracking module, in turn, is configured to be activated in response tothe trigger signal. Further preferably, the trigger signal is generatedexclusively during a predetermined period after that the contentthreshold angle has been exceeded. Thus, for instance in a portabledevice, the eye tracking module may be activated only when it is needed,such as in connection with device rotation. Thereby, the energyresources of the device can be economized.

According to still another preferred embodiment of this aspect of theinvention, the data output module is configured to maintain a selectedorientation in agreement with an orientation in which the visual contentwas presented on the display unit during a preceding period if therotation detection module registers a content attitude angle an absolutevalue of which is less than or equal to an absolute value of a contentthreshold angle. Preferably, provided that the content is rotated in 90degrees increments, it is advantageous to set the absolute value of thecontent threshold angle to a figure slightly above 45 degrees. Namely,thereby, the visual content will continue to have a given orientationalso if the apparatus is tilted back and forth somewhat. Such ahysteresis behavior is beneficial because it avoids undesired shiftingback and forth of the content orientation if the apparatus is held in anattitude angle approximately around the threshold angle.

According to yet another preferred embodiment of this aspect of theinvention, the graphics presentation apparatus is included in a portableelectronic device, which, in turn, contains a main body relative towhich the display unit has a permanently fixed orientation.Consequently, any rotation of the graphics presentation apparatus assuch corresponds to a rotation of the display unit. This facilitates theproposed alignment between the orientation of the visual content and theorientation of the user's eyes.

According to another aspect of the invention, the object is achieved bythe method described initially, wherein image data are registered thatrepresent at least one eye of a user of the graphics presentationapparatus. Based on the registered image data, an orientation of the atleast one eye of the user relative to the display unit is determined. Inresponse thereto, the control signal is generated so that that thevisual content is produced with such orientation of at least one part ofthe visual content that a misalignment between the orientation of the atleast one part and the orientation of the at least one eye of the useris minimized. The advantages of this method, as well as the preferredembodiments thereof, are apparent from the discussion above withreference to the proposed apparatus.

According to a further aspect of the invention the object is achieved bya computer program product, which is loadable into the memory of acomputer, and includes software adapted to implement the method proposedabove when said computer program product is run on a computer.

According to another aspect of the invention the object is achieved by acomputer readable medium, having a program recorded thereon, where theprogram is to control a computer to perform the method proposed abovewhen the program is loaded into the computer.

Further advantages, beneficial features and applications of the presentinvention will be apparent from the following description and thedependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now to be explained more closely by means of preferredembodiments, which are disclosed as examples, and with reference to theattached drawings.

FIG. 1 show examples of how visual content may be rotated on the displayunit of a stationary graphics presentation apparatus according toembodiments of the invention;

FIG. 2 show examples of how visual content may be rotated on the displayunit of a stationary graphics presentation apparatus according toembodiments of the invention;

FIG. 3 show examples of how visual content may be rotated on the displayunit of a stationary graphics presentation apparatus according toembodiments of the invention;

FIG. 4 show examples of how visual content may be rotated on the displayunit of a stationary graphics presentation apparatus according toembodiments of the invention;

FIG. 5 exemplify how visual content may be rotated on the display unitof a portable graphics presentation apparatus according to embodimentsof the invention;

FIG. 6 exemplify how visual content may be rotated on the display unitof a portable graphics presentation apparatus according to embodimentsof the invention;

FIG. 7 exemplify how visual content may be rotated on the display unitof a portable graphics presentation apparatus according to embodimentsof the invention;

FIG. 8 exemplify how visual content may be rotated on the display unitof a portable graphics presentation apparatus according to embodimentsof the invention;

FIG. 9 exemplify how visual content may be rotated on the display unitof a portable graphics presentation apparatus according to embodimentsof the invention;

FIG. 10 shows a block diagram of a graphics presentation apparatusaccording to one embodiment of the invention;

FIG. 11 illustrates, by means of a flow diagram, the general methodaccording to the invention; and

FIG. 12 illustrates, by means of a flow diagram, a method according toone embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIGS. 1 and 2 show a display unit 110 included in a stationary graphicspresentation apparatus according to one embodiment of the invention.FIG. 10 shows a block diagram of the graphics presentation apparatus100, as such, according to one embodiment of the invention.

The display unit 110 is configured to present visual content VC to auser. A data output module 1020 in the graphics presentation apparatus100 is configured to receive graphics data D and a control signal S. Inresponse thereto, the data output module 1020 is configured to producethe visual content VC in such a manner that the visual content VC has aparticular orientation CO relative to the display unit 110.

The graphics presentation apparatus also contains an eye-tracking module120, which in this case, is integrated into the frame of the displayunit 110. The eye-tracking module 120 is configured to register imagedata representing at least one eye of a user of the graphicspresentation apparatus 100. To enhance the image registering capability,the eye-tracking module 120 may include one or more illuminators, 121and 122, for example configured to emit near infrared (NIR) lighttowards a user of the graphics presentation apparatus. Based on theregistered image data, the eye-tracking module 120 is configured todetermine an orientation EO of the at least one eye of the user relativeto the display unit 110. In response thereto, the eye-tracking module120 is configured to generate the control signal S so that it controlsthe data output module 1020 to produce the visual content VC with suchorientation CO that a misalignment between the orientation CO of thevisual content VC and the orientation EO of the at least one eye of theuser is minimized.

In FIG. 1, the visual content VC already has an orientation COessentially matching the orientation EO of the at least one eye uponretrieval, and therefore no adjustment of the orientation CO isnecessary. However, FIG. 2 illustrates a situation where the visualcontent VC is retrieved with a default orientation directed horizontallyto the left, whereas the orientation EO of the at least one eye of theuser is directed +90° thereto, i.e. upwards. Consequently, theeye-tracking module 120 generates the control signal S so that itcontrols the data output module 1020 to produce the visual content VCwith an orientation CO that is rotated +90° in relation to the defaultorientation. Thus, the orientation CO of the visual content VCautomatically becomes aligned as much as possible with the orientationEO of the at least one eye. This, of course, enhances theuser-experience of the visual content VC.

FIG. 3 shows a display unit 110 included in a stationary graphicspresentation apparatus according to another embodiment of the invention.Here, instead of being integrated into the display unit 110, a separateunit 125 holds the eye-tracking module 120. Such a design is useful whenupgrading a system already having screen to incorporate the invention.

The example illustrated in FIG. 3 pertains to a case essentiallyopposite to that in FIG. 2. Namely, in FIG. 3, the orientation EO of theat least one eye is directed horizontally to the left, and the defaultorientation CO of the graphics data D representing the visual content VCis directed +90° thereto, i.e. upwards. Thus, after having registeredthe orientation EO of the at least one eye, the data output module 1020generates the control signal S, such that the visual content VC isrotated −90° thereto to become aligned as much as possible with theorientation EO of the at least one eye.

According to one embodiment of the invention, the data output module1020 is configured to produce the visual content VC with an orientationCO relative to the display unit 110, which orientation CO may only bevaried in predefined angular increments, say 90° per increment. Namely,this is very efficient if the display unit 110 has a typical rectangularshape. Although, of course, it is technically possible to rotate thevisual content VC in other increments, this would normally be relativelycomplicated from a programming point-of-view, at least if the entirescreen content is to be rotated.

Consequently, if for instance the visual content VC may only be rotatedin orientations CO with 90-degrees increments relative to the displayunit 110, any misalignment below 45 degrees, represents a minimalmisalignment. In other words, as long as the misalignment between theorientation EO of the at least one eye and the orientation CO of thevisual content VC is below 45 degrees a selected orientation CO will bemaintained. Thus, a misalignment of 42° will not result in any change ofthe orientation CO.

FIG. 4 shows another example of a display unit 110 included in agraphics presentation apparatus according to an embodiment of theinvention, where, again, the eye-tracking module 120 is included in aunit 125 separated from the display unit 110. Here, the graphical userinterface presented on the display unit 110 contains a part 410 (e.g. anon-screen window) for presenting visual content (e.g. an image or avideo sequence) with an angle that is adaptively adjustable to theorientation EO of the at least one eye in increments other than 90°,e.g. continuously. This means that, if for example the eye-trackingmodule 120 registers an orientation EO of the at least one eye that is−50° to a vertical reference angle, the data output module 1020 producesthe visual content VC so that this content also attains an angle of −50°to the vertical reference angle, and thus the misalignment between theorientation CO of the part 410 of the visual content VC and theorientation EO of the at least one eye of the user is minimized.

FIGS. 5 and 6 show an embodiment of the invention where the graphicspresentation apparatus 100 is included in a portable electronic devicecontaining the proposed graphics presentation apparatus. Here, theeye-tracking module 120 is preferably included in a main body of theportable electronic device.

FIG. 5 illustrates a use case when a user is presumed to hold theportable electronic device with the display unit 110 in landscape mode,i.e. oriented such that the horizontal width exceeds the vertical height(for a display unit having an aspect ratio other than 1:1). Then, inFIG. 6, it is presumed that the user has rotated the portable electronicdevice +90° to instead be positioned in portrait mode, i.e. orientedsuch that the vertical height exceeds the horizontal width (for adisplay unit having an aspect ratio other than 1:1. Since, here, theuser maintains his/her eyes orientated EO in the same direction, sayupwards, while repositioning the device from the position shown in FIG.5 to the position shown in FIG. 6, according to the invention, theeye-tracking module 120 generates the control signal S in such a mannerthat the data output module 1020 causes the visual content VC to berotated −90° with respect to the display unit 110 to compensate for therotation of the display unit 110 relative to the orientation EO of theuser's eyes.

Of course, the opposite is also possible, i.e. that the user holds theportable electronic device in a fixed position, and instead changeshis/her own posture relative thereto. In this case, the eye-trackingmodule 120 again generates the control signal S in such a manner thatthe data output module 1020 causes the visual content VC to be rotatedwith respect to the display unit 110 to compensate for relative rotationof the orientation EO of the user's eyes. In other words, according tothe invention, the visual content VC always follows the orientation EOof the user's eyes regardless of how the display unit 110 as such isoriented.

Referring now to FIG. 10 again, the graphics presentation apparatus 100may further include a rotation detection module 1010. This module isconfigured to register a content attitude angle αC representing an anglebetween the orientation CO of the visual content VC and a frame ofreference FoR external to the graphics presentation apparatus.Typically, the frame of reference FoR is the Earth's field of gravity.However, other reference systems are also conceivable, such as magneticfields. Here, the data output module 1020 is configured to produce thevisual content VC in such a manner that it is presented with anorientation CO and a format that may depend on the content attitudeangle αC. For example, by default the data output module 1020 may causethe orientation CO of the visual content VC to counter rotate in orderto compensate for a rotation of the display unit 110 (i.e. essentiallyas the prior-art solutions). The graphics presentation apparatus 100then temporarily activates eye-tracking module 120 to check if theorientation CO of the visual content VC is aligned as much as possiblewith the orientation EO of the user's eyes. If required, the data outputmodule 1020 thereafter adjusts the orientation CO of the visual contentVC.

Specifically, according to one embodiment of the invention illustratedwith reference to FIG. 9, the rotation detection module 1010 isconfigured to generate a trigger signal TR if an absolute value of thecontent attitude angle αC exceeded an absolute value of a contentthreshold angle αC_(th) relative to the frame of reference FoR during athreshold time. The eye tracking module 120 is configured to beactivated in response to the trigger signal TR, i.e. the eye trackingmodule 120 is in a passive, or de-activated, mode until it receives thetrigger signal TR. Consequently, substantial amounts of energy can besaved relative to having the eye tracking module 120 continuouslyactivated. Such economizing of the energy resources is especiallyimportant in a battery powered device, such as a portable electronicdevice (e.g. in the form of a laptop computer, a tablet computer, anultrabook, an all-in-one desktop computer, or a smartphone).

Moreover, to further conserve energy, the rotation detection module 1010is preferably configured to generate the trigger signal TR exclusivelyduring a predetermined period after that the content threshold angleαC_(th) has been exceeded. Namely, during periods of a constant, oressentially constant, content attitude angle αC it is reasonable toexpect that the angular relationship between the orientation CO of thevisual content VC and the orientation EO of the at least one eye remainsunchanged.

Therefore, according to one embodiment of the invention, the data outputmodule 1020 is configured to maintain a selected orientation CO inagreement with an orientation in which the visual content VC waspresented on the display unit 110 during a preceding period if therotation detection module 1010 registers a content attitude angle αChaving an absolute value less than or equal to the absolute value of thecontent threshold angle αC_(th). Otherwise, however, the rotationdetection module 1010 sends the trigger signal TR to the eye trackingmodule 120, thus activating this module.

To provide a stabilizing hysteresis behavior, the content thresholdangle αC_(th) may be set to a suitable figure. Assuming that the visualcontent VC can be rotated in 90 degrees increments on the display unit110, it is advantageous to assign the absolute value of the contentthreshold angle αC_(th) a figure slightly above 45 degrees. Namely,thereby, the visual content VC will continue to have a given orientationOC also if the display unit 110 is tilted back and forth somewhat.Consequently, undesired shifting back and forth of the contentorientation is avoided if the apparatus is held in an attitude angleapproximately around the content threshold angle αC_(th). For example, acontent threshold angle αC_(th). =48° results in 6° hysteresis.

Preferably, the graphics presentation apparatus 100 contains, or iscommunicatively connected to, a memory unit 1050 storing a computerprogram product PP, which contains software for controlling theapparatus 100 to perform the above-described actions when the computerprogram product PP is run on at least one processing unit of theapparatus 100.

Naturally, although FIGS. 1 to 9 show specific examples of combinationsof the eye-tracking module 120 being included in a separate unit 125 orintegrated into a display unit 110, (stationary or portable), anglerelationships and rotation directions for the orientation CO visualcontent VC, according to the invention, any other combination of theeye-tracking module 120 being included in a separate unit 125 orintegrated into the display unit 110, angle relationships and rotationdirections for the orientation CO visual content VC is equally possible.

In order to sum up, we will now describe the general method according tothe invention with reference to the flow diagram in FIG. 11.

In a first step 1110, visual content VC is presented on a display unit110. In parallel there with, image data are registered representing atleast one eye of a user watching the visual content VC. Based on theregistered image data, a step 1120 then checks if a misalignment betweenthe orientation EO of the at least one eye and an orientation CO of thevisual content VC is minimal. In other words, step 1120 investigates ifthe visual content VC is aligned as much as possible with the eyeorientation EO. If the misalignment between the orientations EO and COis not minimal, a step 1130 follows. Otherwise, the procedure loops backto step 1110.

Step 1130 causes at least one part of the visual content VC to rotaterelative to the display unit 110, such that the misalignment between theorientation CO of the at least one part of the visual content VC and theorientation EO of the at least one eye becomes minimal. Thereafter, theprocedure loops back to step 1110.

Specifically, to effect the content rotation in step 1130, an eyetracking module 120 feeds a control signal S to a data output module1020, which causes the data output module 1020 to produce the visualcontent VC with the desired orientation CO on the display unit 110.

FIG. 12 illustrates a preferred embodiment of the method according tothe invention. Here, in a first step 1210, visual content VC ispresented on a display unit 110. A step 1220 thereafter checks if theabsolute value |αC| of a registered content attitude angle αCrepresenting an angle between the orientation CO of the visual contentVC and an external frame of reference FoR has exceeded an absolute value|αC_(th)| of a content threshold angle αC_(th) during a threshold time,and if not, the procedure loops back to step 1210 (assuming that it isnot necessary to alter the orientation CO of the visual content VC).

However, if in step 1220 it is found that the absolute value |αC| hasexceeded the absolute value |αC_(th)| during the threshold time, a step1230 follows in which an orientation EO is determined of at least oneeye of a user watching the visual content VC. The orientation EO isdetermined based on image data registered by an eye tracking module.Preferably, step 1230 involves activating the eye tracking module, whichup until then preferably has been de-activated.

Subsequently, a step 1240 follows, which checks if a misalignmentbetween the orientation EO of the at least one eye and an orientation COof the visual content VC is minimal. If the misalignment between theorientations EO and CO is not minimal, a step 1250 follows. Otherwise,the procedure loops back to step 1210. Step 1250 causes at least onepart of the visual content VC to rotate relative to the display unit110, such that the misalignment between the orientation CO of the atleast one part of the visual content VC and the orientation EO of the atleast one eye becomes minimal. Thereafter, the procedure loops back tostep 1210.

All of the process steps, as well as any sub-sequence of steps,described with reference to FIGS. 11 and 12 above may be controlled bymeans of a programmed computer apparatus. Moreover, although theembodiments of the invention described above with reference to thedrawings comprise a computer apparatus and processes performed in acomputer apparatus, the invention thus also extends to computerprograms, particularly computer programs on or in a carrier, adapted forputting the invention into practice. The program may be in the form ofsource code, object code, a code intermediate source and object codesuch as in partially compiled form, or in any other form suitable foruse in the implementation of the process according to the invention. Theprogram may either be a part of an operating system, or be a separateapplication. The carrier may be any entity or device capable of carryingthe program. For example, the carrier may comprise a storage medium,such as a Flash memory, a ROM (Read Only Memory), for example a DVD(Digital Video/Versatile Disk), a CD (Compact Disc) or a semiconductorROM, an EPROM (Erasable Programmable Read-Only Memory), an EEPROM(Electrically Erasable Programmable Read-Only Memory), or a magneticrecording medium, for example a floppy disc or hard disc. Further, thecarrier may be a transmissible carrier such as an electrical or opticalsignal which may be conveyed via electrical or optical cable or by radioor by other means. When the program is embodied in a signal which may beconveyed directly by a cable or other device or means, the carrier maybe constituted by such cable or device or means. Alternatively, thecarrier may be an integrated circuit in which the program is embedded,the integrated circuit being adapted for performing, or for use in theperformance of, the relevant processes.

The term “comprises/comprising” when used in this specification is takento specify the presence of stated features, integers, steps orcomponents. However, the term does not preclude the presence or additionof one or more additional features, integers, steps or components orgroups thereof

The invention is not restricted to the described embodiments in thefigures, but may be varied freely within the scope of the claims.

This application claims priority to EPO Application No. 12196926.5 datedDec. 13, 2012; the contents of which are hereby incorporated herein byreference.

What is claimed is:
 1. A non-transitory machine readable medium havinginstructions stored thereon for controlling an eye tracking device,wherein the instructions are executable by one or more processors to atleast: determine a frame of reference; determine, for content displayedon a display device, a content angle relative to the frame of reference;and activate a passive or deactivated eye tracking device upon thedisplay device being oriented such that the content angle exceeds athreshold angle relative to the frame of reference.